Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

849
FXUS63 KLOT 271134
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
534 AM CST Thu Nov 27 2025

.KEY MESSAGES...

- Winter storm watch has been issued for late Friday night
  through Saturday night for all of northern and central IL as
  well as extreme northwest Indiana.

- Impactful snow is likely late Friday night through Saturday
  night. It remains too early for specific snowfall amounts and
  locations, but there is >60% chance for 6"+ amounts and
  higher end travel impacts in portions of the area.

- Well below normal temperatures will persist into or through
  next week, perhaps with additional chances for snow (Monday
  night).

&&

.DISCUSSION...
Issued at 314 AM CST Thu Nov 27 2025

Through Friday:

Extensive stratus deck is blanketing the area this morning with
plenty more stratus upstream. As is so often the case, guidance
is doing an exceptionally poor job handling this wrap around
cold air advection stratus, and for this reason have trended
toward a much cloudier forecast today into this evening. There
will probably be a few breaks in the overcast, but overall
mostly cloudy conditions are expected.

GOES IR and low level water vapor imagery both depict a vort
max over northwest MN early this morning. RAP seems to have
initialized this feature decently and has it zipping southeast
to southern WI by this afternoon. Slightly colder cloud tops are
evident on IR imagery with this feature and quite a few sfc
obs reporting flurries, so certainly seems plausible that there
could be some flurries leaking out of the stratus deck this
afternoon across northeast IL and northwest IN.

Speaking of northwest Indiana, guidance does show boundary layer
winds veering from a west-northwesterly to more of a
northwesterly direction this evening in the wake of a weak sfc
trough. This could allow lake effect snow showers to build back
west into northeastern Porter County tonight with a chance of
some minor accumulation even over far northeast Porter County.

Otherwise, look for some subsidence tonight in the wake of the
shortwave which could *maybe* encourage some breaking up and
dissipation of the stratus deck overnight. If stratus doesn`t
clear out tonight, it likely will Friday morning with some
sunshine expected Friday.

Temps today into this evening should largely flatline under the
stratus with only a 2-4F diurnal swing. Assuming stratus does
indeed break up tonight, colder temperatures are expected.
Sunshine should be pretty ineffective at warming things up Friday
with highs still only expected to reach into the low to mid 30s.

- Izzi

Friday Night through Wednesday:

In collaboration with neighboring offices, we have opted to
hoist a Winter Storm Watch for all of northern IL and far
northwestern IN from late Friday night through early Sunday
morning.

The typical uncertainties that go with the forecast of
accumulating snowfall at a 48+ hour lead time persist.
Nevertheless, confidence continues to grow that much of the area
will experience an impactful accumulating snowfall late Friday
night through Saturday night. At the present time, there is a
60%+ chance of snow amounts exceeding 6" across a vast majority
of the area. Admittedly, even if snow amounts underperform with
this event, the threat of hazardous travel is still very likely
during the busy holiday weekend. Accordingly, we have opted to
pull the trigger on a watch.

A strong short-wave trough off the WA/OR coast this morning
will come ashore later today into tonight. Thereafter, in
response to amplifying ridging into the Gulf of Alaska, this
impulse will dig into the central and southern Rockies and
foster lee surface cyclogenesis near the OK Panhandle into
Friday evening. The surface low will then track east-
northeastward across the lower MO Valley and over the the mid MS
Valley region Saturday into Saturday evening.

The combination of increasingly diffluent upper-level flow
within the entrance region of an upper-level jet over the Great
Lakes and the onset of robust and deep low-to mid-level
WAA/isentropic upglide will foster the development of a sizable
precipitation shield (primarily in the form of snow) across the
Midwest Friday night into Saturday. Across our area, the onset
of snow should occur sometime after midnight Friday night. Once
it begins, widespread accumulating snow is a good bet through
the day Saturday. Peak snow rates during this event could end up
around, or a bit over an 1" per hour. At the present time,
these higher rates look to be most favored sometime from late
morning through early Saturday evening. Ultimately, however,
this time window will be dependent on the actual speed of the
system, which is still not entirely clear, so this general
timeframe could change. Snow rates should gradually diminish
Saturday night into early Sunday morning as the main storm
system shifts into the the eastern Great Lakes.

As can be expected, assessing total snowfall amounts remains a
challenge with this system owing to the magnitude of QPF and
variability in snow ratios (exact track of the low), and the
potential for some areas (particularly in my far south) to mix
with rain Saturday evening. Overall, snow ratios continue to
favor around the typical 10-13:1. However, across my far
southern areas (Livingston, Ford, Iroquois, Newton, Jasper and
Benton counties) there remains a play where enough warm air gets
driven northward ahead of the surface low into Saturday evening
to allow the snow to mix with or change to rain, or at very
least result in lower liquid to snow ratios for a period. If
this occurs, total snow amounts in this region would be limited
(at least to some degree) compared to areas that remain all snow
farther north. It is recommended to monitor for forecast
updates and, if necessary, consider adjusting travel plans.

The main snow shield should quickly exit to the east Sunday
morning, leaving a period of strong CAA and flurries from
shallow stratocumulus. Conditional on the presence of the fresh
snowpack over the weekend, clearing skies and diminishing winds
with an approaching surface ridge will promote a rather chilly
Sunday night with lows potentially at or below zero across
interior northern Illinois. Very cold conditions will persist
through Tuesday as a reinforcing shot of colder air arrives on
Monday. A mid-level wave crossing the Ohio River Valley late
Monday afternoon and Monday night may brush southern portions of
the forecast area with light snow. Sub-zero low will again be
possible Monday night if the aforementioned system remains
solidly south of the area.

KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 534 AM CST Wed Nov 26 2025

- Gusty WNW winds will continue, with occasional gusts to 30kt
  possible today.

Gusty WNW winds will continue today and probably into this
evening with occasional gusts to around 30kt today. Expecting
mostly BKN-OVC conditions to continue into this evening, though
a hole in the stratus has opened up recent to the west of the
terminals which could result in a period of partial clearing
this morning. Can`t rule out a few flurries this afternoon into
early this evening, but not expecting any meaningful impacts to
VSBY. Stratus is expected to break up tonight and once CIGs
break up, winds should respond by decreasing and losing their
gusts.

- Izzi

&&

.MARINE...
Issued at 314 AM CST Thu Nov 27 2025

Winds have eased some over the lake since earlier Wednesday
evening, however gales are still occurring over the open lake
and into the Indiana nearshore waters, especially east of Gary.
With the Chicago Crib no longer reporting gales and with winds
expected to very slow ease today, seems the gale threat for the
IL waters has diminished and planning to downgrade to a small
craft advisory there. For the Indiana water with a longer fetch,
no changes planned to the gale warning, but certainly possible
the day shift may be able to transition to a SCY earlier than
the current 03z Friday expiration time.

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Watch from late Friday night through late
     Saturday night for ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-
     ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-
     ILZ108.

IN...Winter Storm Watch from late Friday night through late
     Saturday night for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 4 AM CST Friday for the IL
     nearshore waters.

     Gale Warning until 10 PM CST this evening for the IN nearshore
     waters.

&&

$$

Visit us at weather.gov/chicago